Blender does not update the file's information when rendering
I can replicate that in Windows 10 and the default Explorer window. By creating a basic animation with the default Cube in Green and then re-rendering with Red.

If I check the resulting file Properties then, the Date Modified and Date Accessed values are updated correctly. 

This is expected behaviour. Windows is only showing the Created Date

In Explorer you can go to the View menu and click Add Columns to add Date Modified and "Choose Columns" to add Date Accessed. 

From what I can tell, this is when Windows decides the folder you are in is designated"Photos", as all my other folders default to show Date Modified.

/me shakes fist at Microsoft